Re: [PATCH] vgacon: Add support for soft scrollback

[Jindrich Makovicka <makovick@kmlinux.fjfi.cvut.cz>]

Antonino A. Daplas wrote:
> The scrollback buffer of the VGA console is located in VGA RAM. This
> RAM is fixed in size and is very small. To make the scrollback buffer
> larger, it must be placed instead in System RAM.
> 
> This patch adds this feature.  The feature and the size of the buffer
> are made as a kernel config option.  Besides consuming kernel memory,
> this feature will slow down the console by approximately 20%.
> 
> Signed-off-by: Antonino Daplas <adaplas@pol.net>
> ---
> 
> This patch is the result of a discussion on how to capture very long
> oops tracings.  One of the suggestions was to increase the size of
> the scrollback buffer of the VGA console.
> 
> I haven't tested the code rigorously, so let me know of any bugs. I
> also tried to make it behave as close as possible to vgacon with a hard
> scrollback.

[...]

> +static int vgacon_scrolldelta(struct vc_data *c, int lines)
> +{
> +	if (!lines)		/* Turn scrollback off */
> +		c->vc_visible_origin = c->vc_origin;
> +	else {
> +		int margin = c->vc_size_row * 4;
> +		int ul, we, p, st;
> +
> +		printk("vgacon delta: %i\n", lines);

                ^^^^^^
This disables the hard scrollback, as the console is immediately
scrolled back when the mesage gets printed.

Regards,
-- 
Jindrich Makovicka